Currently, various technologies are developed and applied to satisfy globally tightened exhaust gas regulations. In particular, research is being actively conducted on a gasoline direct injection (GDI) engine for directly injecting a high-pressure fuel into a combustion chamber so as to increase combustion efficiency, to reduce an exhaust gas, and to improve fuel efficiency and an output.
A high-pressure pump and a direct injector for injecting a high-pressure fuel are already developed by a plurality of well-known companies, and a fuel rail for stably supplying a fuel into the direct injector (GDI) is being individually developed according to the position and space of an engine.
In a multi port injection (MPI) or port fuel injection (PFI) engine for injecting a fuel into an intake port or valve, combining the fuel with fresh air, and supplying a mixed gas into a combustion chamber, since a low fuel pressure, e.g., 3 to 5 bar, is applied to a fuel rail, development of fuel rails is more focused to ensure reliability regarding vibration and fuel pulsation in a fuel rail rather than to ensure rigidity against a fuel pressure. However, in order to develop GDI fuel rails having a high fuel pressure, e.g., 120 to 200 bar, resistance against fatigue fracture generated due to pressure, vibration, and heat has to be ensured first.
In a conventional GDI fuel rail, a mount unit and an injector cup are independently formed and are individually bonded to a main pipe by using a brazing method (using a filler metal).
However, in that case, due to pressure, vibration, or heat generated by an engine, a fuel rail is displaced and thus a fatigue stress is applied to each component of the fuel rail. In particular, stress is concentrated on brazed parts of a mount unit and an injector cup fixed to an engine head.